A downhole safety valve is placed at a predetermined distance below the surface of an oil well. Should a fire break out at or near the wellhead, the downhole valve is closed by terminating the fluid pressure to the downhole valve, the valve being located in the production tubing.
To impose the required hydraulic fluid pressure on the downhole valve, a stainless steel tubing, about 1/4" in diameter, is extended from the source of the hydraulic fluid pressure to the valve. There are various obstructions to the flow of hydraulic fluid from the source. The wellhead structure must be penetrated and the source of fluid is linked with the 1/4" stainless steel tubing as it extends down to the downhole valve.
Once the conduit or path for the hydraulic fluid is extended through the wellhead structure, there is no provision available for controlling the fluid pressure extending to the downhole valve. Therefore, there is a need in this art for a simple, effective temperature-responsive structure which will carry out a program to control communication between the source of the hydraulic fluid pressure and the 1/4" stainless steel tubing whose upper end is communicated with the conduit penetrating the wellhead structure. When released from this pressure, the downhole valve closes. When the valve is closed, fuel to the fire at the wellhead is deprived of the inflammable production which would sustain or enlarge the fire.